Fighting around the western city of Duekoue was one of the French force's heaviest engagement yet in the three-month-old rebellion splitting their former West African colony, the world's largest cocoa producer and the region's economic powerhouse.

The battle highlighted how the stepped-up French deployment may be decisive in stopping the rebel campaign to drive out President Laurent Gbagbo and seize the entire country.

The rebels have scored several days of success in their push south and east toward Abidjan. Controlling the city is the key to controlling Ivory Coast, a country of high-rises, highways, and international businesses, and one of Africa's most vital economic hubs and ports.

With so much at stake for the region if Ivory Coast falls into chaos, the French decided to take up their largest military role in years in their former colonial empire.

As rebels seized the far west city of Man on Thursday and pushed farther south Friday, French forces dug in at the western city of Duekoue, 210 miles northwest of Abidjan.

Fighters of the French Foreign Legion and other elite troops had set up position with anti-tank missiles, rocket launchers and heavy machine guns outside Duekoue to stop any rebel advance _ calling their positions in the area the "stop-point" for any insurgent drive on the commercial capital.

Saturday, rebels moved to bypass the French.

In hours of fighting Saturday with Ivory Coast government forces, rebels took the town of Blodi, just outside Duekoue, on a secondary road that would let them skirt the French position and push on to Abidjan.

Ivory Coast's forces initially fled, leaving 40 French troops posted near Blodi to face a fast-moving convoy of rebels in pickup trucks and other vehicles, French Capt. Hubert Dunant said.

The French fired one warning shot, and a second. When the rebels responded with assault rifle fire, Dunant said, French forces blasted the lead rebel vehicle with fire from a light-armored tank.

French tanks destroyed two cars behind, Dunant said. While light-arms fire drove back French who tried to inspect the destroyed vehicles, they saw one body and one rocket launcher. Soldiers think four to seven other rebels were killed, their bodies taken away by comrades, he said.

French authorities in Abidjan described the encounter as a rebel "ambush." Rebel leader Felix Doh, a commander in the west, denied that, saying rebels happened upon the French while chasing fleeing government forces.

The battle reached within a half-mile of Duekoue. Sounds of guns and mortars sent civilians fleeing or hiding indoors.

French troops based at a school outside the city spilled out to the fighting in light armored vehicles with mounted cannons. Other troops loaded mortars on trucks.

Despite gains during the day, rebels by nightfall had pulled back eight miles north of Duekoue, the rebel commander said.

The French said they suffered no injuries. There was no immediate information of rebel or government casualties.

French forces, initially in Ivory Coast to protect foreign nationals and enforce a shattered cease-fire, stepped up their role as the rebel challenge grew. France plans to double its deployment to 2,500 by year's end.

Ivorian rebels took up arms Sept. 19 with an unsuccessful coup attempt but quickly seized the northern half of the country. An Oct. 17 cease-fire stalled fighting in the north, but a second, a western front emerged in recent weeks, threatening Abidjan from a second side.

Rebels in the west have not entered peace talks. And their ranks include fighters from neighboring Liberia, known for raping and looting among civilians.

Government forces have been weakened by defections of hundreds of disgruntled army officers, joining a northern core of rebels who accuse President Laurent Gbagbo's southern-based government of discrimination against their ethnic groups.

French forces fought the rebels once before in a November clash that killed 10 rebels and one French fighter.

For decades West Africa's most prosperous and stable nation, Ivory Coast has fallen into political turmoil and ethnic, political and regional violence since a late 1990s economic downturn followed by a 1999 coup, the country's first-ever.

Rebels demand that Gbagbo resign. Gbagbo took office during a 2000 election that Gen. Robert Guei, leading of the coup-installed military junta, tried to steal. Violence cut short the vote, and a people's revolt put Gbagbo in power.